1. Field of the Invention
This invention relates to the shaping and cooling of sheets and particularly in the high speed production of bent glass sheets that are toughened by air quenching, and most particularly, for shaping and heat treating relatively thin glass sheets. However, this invention is also suitable for use in the transfer of sheets of any flexible or moldable material from an upper, shaped vacuum holding member that holds a shaped sheet by vacuum against an apertured lower shaped wall thereof to a lower supporting member disposed below the lower, apertured, shaped wall by releasing the vacuum that provides the suction support without introducing tilting of the sheet (during its transfer) of a magnitude that causes misalignment between the transferred sheet and said supporting member during its free fall from said upper shaped vacuum holding member to said lower supporting member.
Shaped glass sheets are widely used as side windows in vehicles such as automobiles or the like and, to be suitable for such application, flat glass sheets must be shaped to precisely defined curvatures dictated by the shape and outline of the frames defining the window openings into which the glass side windows are installed. It is also important that the side windows meet stringent optical requirements and that the windows be free of optical defects that would tend to interfere with the clear viewing therethrough in their viewing area. During fabrication, glass sheets intended for use as shaped windows in vehicles are subjected to thermal treatment to temper the glass for strengthening the same and increasing the resistance of the shaped window to damage resulting from impact. In addition to increasing the resistance of a glass sheet to breakage, tempering also causes a glass sheet to fracture into relatively small, relatively smoothly surfaced fragments that are less injurious than the relatively large, jagged fragments that result from the more frequent breakage of untempered glass.
The commercial production of shaped glass sheets for such purposes commonly includes heating flat sheets to the softening point of the glass, shaping the heated sheets to a desired curvature and then cooling the bent sheets in a controlled manner to a temperature below the annealing range of the glass. During such treatment, a glass sheet is conveyed along a substantially horizontal path that extends through a tunnel-type furnace where the glass sheet is one of a series of sheets that are heated to the deformation temperature of glass and into a shaping station where each glass sheet in turn is transferred onto a lifting member that lifts the glass sheet into engagement with a vacuum mold. The vacuum mold holds the shaped glass by suction while the lifting member retracts to below the substantially horizontal path. At about the same time, a transfer and tempering ring having an outline shape conforming to that of the glass sheet slightly inboard of its perimeter moves upstream into a position below the vacuum mold and above the lifting member. Release of the vacuum deposits the shaped glass sheet onto the tempering ring.
When prior art apparatus transferred a shaped glass sheet from the vacuum mold onto the transfer and tempering ring in misaligned or misoriented relation to the latter, the glass sheet shape would depart from required tolerances. No provision was available to remedy such a defect except to destroy the article so produced in order to avoid a customer complaint. In addition, while prior art apparatus kept improving the speed of glass sheet bending and tempering, there still remained a need for further improvement, particularly in the shaping and tempering of thinner glass sheets than those required prior to the need to supply thinner tempered glass windows for automobiles in order to lighten the vehicle, thereby reducing its rate of fuel consumption.
2. The Prior Art
U.S. Pat. No. 1,478,126 to J. A. Lewis and A. C. Crimmel discloses and claims a suction head so proportioned that it can be inserted into a mold so as to contact an article formed within the mold. When suction is applied to the vacuum head, the article can be lifted from the mold by lifting the vacuum head while a blower fan operates through a flexible tube connected to the vacuum head to set up a suction in the vacuum head. A relief opening normally closed by a valve is provided to break the suction so that the article may be deposited on a suitable support. It is necessary to provide the valve with a handle to slide the valve away from the relief opening so that air can enter the vacuum head and relieve the article from the suction.
U.S. Pat. No. 3,004,295 to Paul H. Bottoms, John G. Stansbury and Robert J. Clapp uses suction to hold a flexible, impervious film against the upper surface of a hot blank of plastic material while the bottom surface of the blank is held in curved form against the upper curved surface of a die. In every embodiment of this patent, it is necessary to lift the shaped sheet from the upper surface of the die after vacuum is discontinued.
U.S. Pat. No. 3,279,906 to Robert N. Baker provides apertured press faces for molds that shape glass sheets by press bending. The molds are in the form of air chambers whose front walls are the press faces. The latter have complementary shapes and form a hot glass sheet to such a corresponding shape while engaged between the molds. Air under pressure passes through the apertures in the apertured press faces to provide a thin air film between each mold and the glass sheet during shaping and to chill the glass sheet sufficiently rapidly to impart a temper therein. Tongs grip the glass sheet during its shaping and tempering.
U.S. Pat. No. 3,567,265 to Wendell S. Blanding and Richard F. Kruger uses a vacuum head to remove a shaped article from the upper surface of a mold by first applying vacuum to lift the article off the mold and into contact with fingers and then lifting the head with the article further from the mold. Release of the vacuum permits the release of the article from the vacuum head and its deposit onto a table or platform means.
U.S. Pat. No. 3,634,059 to Richard C. Miller and U.S. Pat. No. 3,607,188 to George W. Stilley and Herbert W. Eilenfeld apply pressure through apertures in a downwardly facing convex shaping surface to help disengage a concavely shaped upper surface of a shaped glass article.
U.S. Pat. No. 3,846,104 to Samuel L. Seymour and U.S. Pat. No. 4,092,141 to Robert G. Frank and DeWitt W. Lampman lift a heat-softened glass sheet into engagement with a vacuum shaping mold having a downwardly facing apertured shaping surface. Vacuum is applied to hold the lifted glass sheet by suction against the downwardly facing shaping surface of the vacuum shaping mold until the lifting means is removed and a transfer ring-like member shaped in elevation and outline to conform to the sheet is moved to a position beneath the vacuum shaping mold. Release of the vacuum drops the shaped glass sheet onto the shaped transfer ring-like member. Sometimes, the shaped glass sheet would deposit in misaligned relation to the ring-like member.
The prior art patents just enumerated fail to provide means at the shaping station to insure that each shaped glass sheet is oriented and aligned on the tempering ring in proper orientation and alignment thereon so that it retains its proper shape while cooling. A misshaped glass sheet that cannot fit into a shaped frame would be rejected by a customer. Furthermore, the need to bend and temper thinner glass sheets (4 millimeters thick or less) than thicknesses handled previously (4.5 to 6 millimeters) makes it desirable to incorporate means to reduce the time required for the apparatus to complete a cycle of bending and tempering, particularly the time needed to transport a heated glass sheet through a shaping station and completely into a cooling station, because thin, hot glass sheets lose their shape more rapidly than thicker glass sheets and also cool more rapidly to a temperature below which it becomes difficult if not impossible to impart an adequate temper in the glass.
Any additional time needed to correct a misalignment between the released shaped glass sheet and the ring-like member would cause the glass sheet to lose its desired shape and limit the degree of maximum temper possible. Since automobile safety is a function of the degree of temper in certain curved tempered windows in the vehicle, it is desirable to maintain the ability of a tempering line to obtain as high a temper as desired in shaped glass sheets of various thicknesses.